Ex-Situ Remediation of Former Gas Station UST Release

ORIN successfully treated petroleum contaminated soil and groundwater with ex-situ chemical oxidation during a pilot study at a former gas station facility. Petroleum hydrocarbons were reduced from 264,700 ppb to less than 10,635 ppb over a two-week period. ORIN’s approach saved the client approximately $85K over traditional remediation approaches.

Remediation Approach:

Chemistries used during ex-situ remediation

ORIN began ex-situ remediation of soils utilizing Fenton’s Reagent (hydrogen peroxide and an iron catalyst). The Fenton’s Reagent treatment chemistry included the addition of acid to reduce the pH to < 5. The iron catalyst used was ferrous sulfate heptahydrate (FeSO4 • 7H2O).

The preferred Fenton’s Reaction is:

Hydrogen Peroxide + Ferrous Iron ➜ Hydroxyl Radical + Hydroxyl

Ion + Ferric Iron: H2O2 + Fe+2 ➜ OH. + OH- + Fe+3

The hydroxyl free radical is an extremely powerful oxidizer (second only to fluorine) against organic compounds. Residual hydrogen peroxide, due to its unstable characteristics, rapidly decomposes to water and oxygen in the subsurface environment. Soluble iron amendments are precipitated out during conversion to ferric iron.

Summary of Ex-situ Implementation

Ex situ remediation at this site involved the application of the treatment chemistry directly onto the exposed soils. An excavator was present to displace a certain area of soil down to depth. A portion of that soil was then placed back into the excavated hole while the treatment chemistry was being applied to the soil. The excavator would then continually mix the soil and chemicals together until the desired amount of treatment chemistry was applied. More soil was then added from the displaced pile while additional chemical was applied and mixed thoroughly. This process was duplicated until the desired consistency and chemical volume was applied to the entire targeted soil volume.

Effectiveness

Two weeks following treatment, soil samples were taken at various locations within the treatment area. Based on this pilot study, Fenton’s Reagent chemistry reduced the mass of petroleum contamination by greater than 95 percent. Benzene concentrations were reduced from 8,700 ppb to 24 ppb within the pilot test area. Fenton’s Reagent chemistry was found to reduce the petroleum concentrations in the soils below their respective IEPA Tier 1 Commercial Cleanup Objectives.

The Bottom Line

ORIN successfully reduced contaminant levels in the pilot study area by utilizing hydrogen peroxide chemistry throughout the day. Performing the pilot study demonstrated the effectiveness and feasibility for full-scale injection at this site. Therefore reducing full scale costs by $375K and shortening project timeframe by years over traditional remediation approaches.